OIE Update on Ebola Disease Virus in Animals and Humans

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With the latest outbreak of Ebola disease virus which was reported in DR Congo in May 2018, it is evident that these sporadic outbreaks might occur once in a while in the nearest future. This is of public health importance especially in vulnerable communities in West and Central Africa. Therefore, it is important to always stay prepared with the right updated information and tools so as to know how to best combat the disease.

The following information was adapted from OIE (Office internationales des epizootes). It comprises of a holistic and updated information of the Ebola Disease virus and its transmission dynamics in both animals and humans.

1. Aetiology

Ebola virus disease (EVD) is also known as Ebola haemorrhagic fever and is considered to be an emerging zoonotic disease. EVD is a severe contagious disease affecting humans and non-human primates. It can be transmitted to humans through direct contact with tissue, blood, other body fluids, and excretions from an infected human or animal. The causative agent is classified in the genus Ebolavirus of the Filoviridae family. There are several species in the genus Ebolavirus (EBV) these include: Zaire ebolavirus (EBOV); Sudan ebolavirus (SUDV); Bundibugyo ebolavirus (BDBV); Reston ebolavirus (RESTV) and Taï Forest ebolavirus (TAFV). All have been detected in Africa only, apart from RESTV. RESTV was isolated in 1989-90 in Reston, Virginia (USA) from macaques imported from the Philippines. In 2008, pigs from pig farms close to Manilla (Philippines) also tested positive for RESTV.
2. Occurrence
Up to 2013, EVD occurred mainly in remote rainforest areas of Central and East Africa (DRC, Sudan, Gabon, Republic of the Congo and Uganda). West Africa had only been known to be affected by a limited episode of Taï Forest ebolavirus (TAFV) in the Ivory Coast in 1994. However, a severe epidemic, starting in 2013-14, affected a large West African region (mainly in Guinea, Sierra Leone and Liberia). For the first time, the epidemic penetrated densely populated areas including capital cities, increasing the risk of wider spread. Since 2014, three new outbreaks have occurred in the Democratic Republic of Congo till date.
3. Natural hosts
The natural reservoir of Ebola has not yet been confirmed. However, the results of field studies, laboratory research, and epidemiological surveys in Africa strongly suggest that fruit bats may be natural hosts for EBOV and they are currently thought to be the principal animal reservoir. Indeed, research results suggests that some bat species may carry the virus without showing clinical signs of illness. The related Marburg virus has been isolated from fruit bats (Roussettus aegyptiacus) in Uganda.
4. Susceptibility of animal species
Ebola viruses have also been detected in species such as non-human primates (apes and monkeys), and duikers (a small wild antelope). However, non-human primates are not considered as natural hosts because of their high sensitivity to the virus and their high mortality rate when infected. Although the source of infection for non-human primates and duikers remains unclear, most evidence indicates direct infection from one or more natural hosts or their excretions.
Susceptibility of pigs to EBV has been demonstrated in the laboratory setting, but their role in EVD epidemiology is unclear. Antibodies to EBV have been detected in dogs. So far there is no evidence that domestic animals play an active epidemiological role in the transmission of the disease to humans.
5. Introduction to human populations
Ebola virus disease is initially introduced into human populations through contact with infected wild animals to humans and is most likely associated with hunting, collection of sick or dead wild animals and handling or consumption of uncooked bush meat. In rural areas fruit bats are a popular source of forest meat for humans and are prepared by hand to be dried, smoked and/or cooked. Infection of humans through consumption of forest fruits contaminated with bat saliva or faeces is also a suspected transmission pathway.
6. Ebola disease in humans
During EVD outbreaks in humans, human to human transmission occurs through contact with body fluids or excretions of an infected person.
For information about Ebola in humans please refer to the World Health Organization (WHO) Ebola Virus Disease Website and Factsheet, and the CDC Website.



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